1. Field of the Invention
The invention relates to a suspension and to products produced from it.
2. Description of the Related Art
Fumed silica is known for use as thickener and rheological additive. Fumed silica is bulky and exhibits a high degree of interparticulate interaction, and in liquid media produces stable gel states, more particularly at high solids content.
Use as a reinforcing filler in reactive resins and polymer systems, however, necessitates high levels of loading with active fillers which at the same time are particulate thickeners, such as with fumed silica, for example. In many cases, a high thickening action and hence high viscosity and gel state, and hence loss of fluidity, represents a major problem in the processing of active, finely divided, and colloidal fillers. The results are high viscosity, poor fluidity, crepe hardening, lack of pumpability, lack of spreadability, lack of sprayability, inadequate flow in paints, varnishes, and surface coatings, and inadequate processing properties.
It is known that the thickening action of colloidal fillers is associated with OH groups on their surface, and also that oxidic fillers with a high specific surface area are subject to strong Van-der-Waals' interactions, and hence thicken and crepe-harden liquids such as polymers, reactive resins, paints, varnishes, coating materials, adhesives, elastomers, and plastomers, in other words increase their viscosity.
One known way of suppressing the thickening action of metal oxides which at the same time are particulate thickeners is to surface-treat them. In many cases, however, surface treatment may likewise lead to a pronounced rise in the viscosity and in the development of a yield point, as described in EP-A-0686676.